The best way to work out is outdoors. Here, the top reasons to get your sweat on in the summer sun

Think hitting the gym is hard? It's even tougher when the weather beckons you to ditch the four walls and stale air of the indoors for the sun and breeze outside. Stop ignoring your instincts! Nature is a perfect buff-body training ground. Here are seven reasons to blow off the dark, dreary gym and step outside.

Leave the magazines at home and head out for an exploratory run through your 'hood. You'll be surprised how much faster time travels when you aren't in the gym. "Changing your routine, seeing new faces, taking in the scenic shrubberythis all helps combat workout boredom," says Robert Gotlin, DO, director of the Orthopedic and Sports Rehabilitation at Beth Israel Medical Center in New York City. To top it off, a grueling workout may not seem so, er, grueling. "When you're distracted by the environment, you're less aware of your effort, such as how far you've run or how much your quads burn." Heck, you might even double your workout to 60 minutes without even knowing it.

It's easy to get in a fitness rut when your body knows exactly what to expect from your gym machines like the treadmill, elliptical, and stationary bike. The varied terrain of a park might be just what your body need to challenge itself to move in varied, more complex ways, says Stacy Berman, founder and creator of outdoor exercise class, Stacy's Bootcamp. Factor in wind (Mama Nature's form of resistance training), temps (the hotter the weather, the harder your body has to work to cool down), and other external variables, you can end up torching 5 to 7 percent more calories just by trading the treadmill for trails.

Gym memberships aren't cheap. They can drain your bank account—85 percent of Americans spend up to 600 dollars per year on their facilities, and 15 percent pay even more--which can feel like a real waste if you're more of a no-show than gym rat. The smaller investment in a home gym can even be a waste of money for some: American households spend on average 130 dollars annually on sports and exercise equipment. Besides cutting your fitness bills, running out your front door can save you cash on gas.

Playing outside is like organic Prozac. "Breathing fresh air opposed to the recycled kind can create a feeling of euphoria, which comes from the body's release of feel-good endorphins," Gotlin says. "It's not that your muscles respond better to it, but rather your mind does, which in turn makes you want to work harder." Exercising outside also creates greater feelings of revitalization, energy, and positive thinking than does working out indoors, according to a report published in Environmental Science and Technology. What's more, after an 30-minute walk in the park, 71 percent of people feel less stressed, while 72 percent of people who take their walks indoors actually feel more stressed.

Gyms aren't always the meccas of health we make them out to be. A whole slew of studies show that gyms are breeding grounds for germs and bacteria. MRSA is the most dangerous super bug you can catch at your fitness facility—it's resistant to most antibiotics and can cause fever, rash, wounds, and chest pain. Other less harmful infections include athlete's foot, boils, herpes simplex, and ringworm, according to the National Athletic Trainers' Association. You can avoid these hazards by washing your hands often, changing your socks daily, using foot powder, wiping down equipment before and after use and wearing flip flops in the shower. Or you can simply take your training to the streets (even Rocky left the boxing ring every once in a while to run around his 'hood). Indoor air is two to five time more polluted than outdoor air, according to a study from the Environmental Protection Agency. If you've ever walked into a stinky gym, you know exactly what's up.

Breaking a sweat outside may make you smarter. "Humans were hunter-gatherers and farmers for some 300,000 generations; have been industrialized for only six to eight, so we are outdoor animals living largely inside," says Jo Barton, Ph.D., the lead author of a 2011 study that analyzed the mental health of 53 people who were involved in indoor or outdoor activities for six weeks. "Closeness to nature increases our well-being—it has an immunizing effect by protecting us from future stresses and helping us concentrate and think more clearly," she says.

How's this for empowering: The outdoors is always ready to go. No class schedules, no waiting in line for the elliptical machine, and no need to dig out your exercise bands from the closet. You can fit fitness in whenever you have a chance. Even a 20-minute intense workout in the great outdoors will do the trick: A single high-intensity workout is three times more effective at burning fat than endurance training, according to a study published in Metabolism.